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Old 10-07-2004, 07:41 PM
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oil burning,knocking update.

After lng time and efforts I now know why my 383 stroker was consuming oil at a very high rate and also know the source of a knock that could be heard around the base...I had looked long into different possibilities for the oil burning and always pushed away the basics wich were the oil rings gone...simply as that! Kind of surprising on a fresh (less than 1500 miles) rebuilt but apparently a bad choice of rings coupled with an unmatching honing grit resulted into a quart at every 250 miles....For very long I thought about the PVC sucking in oil,or used valves guides. I've tried many remedies to these supposed guilty ones like installing OEM internal baffles to aftermarket valve covers and even sending the heads for rebuilding...but the darn good old oil rings were the ones!

The last of my problems with this stroker was a knocking...dropped the pan twice,plastiguaged the bearings and what more!? Hours and hours of head scratching and creeping under or around that engine...nothing to find! Finally sent the motor to the shop and now I know: one piston slapping! It's not my intention to discredit hyper. pistons here but that's what was in the block and my machinist just don't like to see them into chevy's blocks as apparently they (the blocks)don't transfer heath in same way that ford's or chrysler's blocks do and the end result is to see more frequently piston slapping into a chevy block as the lesser expansion factor found with Hyper. pistons colaborate to this ...

I surely hope that finally someone who know what he's doing will build that motor right...another testimony as that once one has found a good machinist don't let him go!
Ron.

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Old 10-08-2004, 04:56 AM
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so...you had a rod slapping the block or what?

you said a piston slapping? Do you mean the piston is slapping inside the hole...I don't understand exactly...thanks


Tazz


Rat Rods Rule!
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Old 10-08-2004, 06:18 AM
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TM 454.

If I understood well the machinist one piston's skirt was hitting the cylinder wall ...this caused by possibly a combination of not having the right cylinder wall-piston clearance to start with and the use of Hyperuthetic pistons with their low expansion factor. He suggests to go with forged because of this.
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Old 10-08-2004, 08:36 AM
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Sounds to me like a clearance issue more than a piston issue. Too many people run hypers with no problem. How about your machinist measures all the bores with you watching and you let us know what shows up. Dont trust anyone.....I just learned this lesson the hard way with bad machine work.

chris
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Old 10-08-2004, 09:22 AM
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chris,

You might have a good recommendation here...the problem is the machine shop is 600 miles away! You know when you aren't an expert there is so much given details explained to you that doesn't make evidence!

If I remember good he told me that he rehoned the block to see if he could reuse the same pistons and he was at 4.031 and that was limit to think of reusing the same pistons...but since the KB are flat ones and my heads s'been milled the compression is now at 11 to 1 and that is a lot for my strickly street intended use..so changing pistons is not only based on Hypers not being anygood.

But he clearly said that in his opinion ,based on different expansion-cooling facts. from one block manufacturers to another ones the use of hyper could be a higher risk of piston slapping problem when used with chevys blocks...fords and chrysler not having such higher risk....makes sense or not?? I'm no expert to say about that!

What is the recommended clearance for hypers versus forged??

I guess that short of being an expert mechanic we poor amateur,have to just believe and hope there are still some honest and knowledgeable experts out there still...

Ron.
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Old 10-08-2004, 01:57 PM
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my machinist measures the actual diameter of each piston and bores the cylinders to manufacturers specs. i.e. piston diameter + manufacture clearance.

It means that a overbore on a chevy 350 might be 4.030 on one cylinder and 4.028 on another but it eliminates the piston slap on the cylinder wall in a fresh rebuild.
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